The author points out that the vast majority (though not all) bunker enthusiasts are male, and offers some ideas on why that might be the case. For example:

“From a Freudian psychoanalytic perspective, there is perhaps much that could be made of the focus, within this culture, of the shelter-as-womb and the preoccupation with penetration and return to that protective space.”

and/or possibly because of, or connected with:

“[…] a peripatetic nostalgia borne of a medley of factors: a primal urge to retreat to a place of (defensive) shelter, a nostalgia for a time where male roles had more clarity and importance (e.g. as ‘defender’), the alienation of deindustrialisation, the move away from a culture of ‘making things’ and a desire in retirement or redundancy to return to or to protect the working-life material places and artefacts that formerly gave life (and male identity) meaning.”

Note: Improbable apologises for the late notice regarding an event in a (somewhat) related field which is cited in the paper : Shedism. The International Men’s Sheds Festival 2014 was held October 3rd – 5th, 2014, Dublin, Ireland,